do i have too much carb?

[taco502001]

Ok I have been having this problem with my car since July of this year where the car keeps fouling out the plugs and i mean fast. I recently had a shop do alot of work to the car and spent around 2 grand on it and still am fouling out plugs but doesn't seem to happen as fast now.

Here is the setup its in my dodge demon which tips the scales at 3100lbs

440 9.7:1 compression ratio

Forged rods, crank, pistons, recently rebuilt holds great cylinder pressure which is the same across the board

ported and polished open chamber 906 heads

this info from comp cams
HYDRAULIC-Serious street/strip effort.
Hyd. Hyd. 3000 to 6200 21-242-428 292H
intake292 exh292 intake/exh@.050 244 244 lift.501 .501 lsa110°
383 needs 3000-3500+ stall. 440 needs
2500-3000. 750 to 800 CFM carb. &
headers 3.91 gear up.

Intake is single plane weiand team g

Carb 825cfm Race Series Demon carbeurator

Hooker 2" fenderwells to 3.5" exhaust

Junk B&M 3k stall

8 3/4 3:23 suregrip rear end

Built manual reverse valve body 727

Complete MSD setup and cleaned up all wiring


I have tested the voltage to wires right at the box the large red and small red see a minimum of 12.25 volts at idle it increases as the rpms increase, timing is locked out at 32*, has new blaster2 coil, taylor thundervolt50 wires, ngk fr7 plugs gapped at .018. I understand that my voltage should be more steady but i think the march pulleys have something to do with it.

Anyways lately the car is still running way too rich and having carb backfires which normally points to timing but it is locked out at 32*, plus if it was electrical or timing wouldn't problem be there the whole time not just after i have driven the car around for a while. I was also told that with the race series carb that when held at part throttle for a while due to mech secondaries and boosters and **** that it just dumps the fuel in when there is no real need for it. If this is true that part throttle driving can cause problems could it be the 2+ hrs of driving it around on the highways at 3000 rpms that fouled the plugs out and that there is really nothing wrong

 

[Mopower71]

Some thing that strikes me is that you have the plugs gapped at .018"
Why such a small gap?
I run .045" on my 440 with MSD and Mopar dist.

 

[Mopower71]

Also, carb backfires are usually due to a lean out condition.

 

[taco502001]

I would like to add that when new plugs are put in this car that it runs strong and will smoke the mickeys all day long.

I think i am going to go with a hotter ngk plug as most of my driving is cruising not full out foot to floor driving.

I am just trying to put my mind at ease as far as finding out the cause, the gentleman i paid close to 2 grand to diagnose the car and fix this problem has told me to check charging system and throttle cable to make sure butterflies are opening all the way. He also mentioned the race series carb can cause a flooding condition at part throttle.

To me i dont think its electrical or ignition as if it was it would be occuring even when new plugs are put in not just after i drive the car around for a while and the plugs become fouled. I mean I tested the wires directly at the msd 6al box and they are seeing minimum of 12.25 volts at idle and increases as rpms increase. Plus the rest of cars wiring was all cleaned up and aftermarket fuse panel installed.

Plus yeah i agree carb backfires is normally a lean out condition, timing, and for msd a rfi/efi problem but as i said if that was the case my problems would be prevalent at all times not just after plugs get fouled. Also my plugs are black all the way its dry thank god but you would think if it was lean condition plugs would be complete opposite.

 

[taco502001]

Also for some strange reason with not doing any changes to the car the other day when i went to start the car fuel started spitting out around the needle seat gasket, I turned the screw in as much as I could which probably was an 1/8 of a turn but it did stop leaking. What would cause that to occur other than just bad gaskets?

 

[C130 Chief]

Your basic combo sounds reasonable with the 850, but I think something is up inside your carb. Have you checked the float levels? What is your fuel pressure? Too much pressure can cause all sorts of grief with flooding, leaking etc... As can a little speck of trash in the carb. You do have a good fuel filter right?

If it were me, I would pull the carb apart and clean/rebuild it. Make sure everything is clean, has new gaskets, THE POWER VALVE IS REPLACED, etc. Since it has been backfiring through the carb, your power valve is possibly blown, causing a really rich condition. Download the manual for your carb (it's pretty informative for setup) read it, and try again.

Now on to the other thing I noticed in your description. "timing locked out at 32 deg" You mean your mechanical advance is locked out and you are timed at 32 degrees all the time ?!? Man, that must be fun to start in the morning! Thats WAY too much advance for low RPM, no wonder it backfires. Try unlocking your advance, run 15 deg initial and 32 total, replace the power valve, set your floats and see what happens.

 

[taco502001]

But if it was timing or an ignition/electrical system problem how come thing runs like raped ape when new plugs are installed no backfiring or cutting out or anything.

It only acts up after driving an extended period of time and that the plugs become fouled. It is the reason why they are becoming fouled that escapes me as i did not perform the work to the carb scott marrison did. He replaced gaskets, power valve etc...

Plus my car turns over really easy with locked out timing, and wouldn't timing being locked out help burn cleaner at idle. Plus my car never overheats or gets hot.

from what i have gathered is plug is a colder burning racing application plug and gap is only at .018, I am going to throw a hotter plug and raise gap. Change battery keep an eye on the voltage make sure msd is getting propper voltage etc...


I am just trying to see if it was just driving on the highway for 2hrs at 3k rpms with this type of carb or if its something more.

 

[rumblefish360]

IMO, I think you have to much carb, even more so with the 3.23's and low(ish) stall.

 

[340mopar]

There is nothing wrong with having your timing locked in at total advance if you can start the car. The springs are so light in my drag car that when it idles at 1100-1200 my timing is all in @ 32. If optimum combustion is @ 32 deg advance it doesn't matter if the engine is rotating at 1200 or 6000 rpm. If it needs 32 deg it needs 32 deg. I believe Demon carbs have a backfire protection system in them but if it has backfired a lot I would still take it apart and check it out.

If you are running a real racing plug then I believe this is were your problem lies in the plug fouling. By looking at your combo I would run a stock style plug for a '70 440, just one heat range colder. You don't have enough compression or power adders to go much lower than that without a fouling problem. After you change plugs then you can work on your jetting. Since it back fires I guessing you are on the lean side but being your plugs are too cold and not cleaning correctly it is giving you a false reading that it is rich.


Chuck

 

[demon seed]

First things first, Install a fuel pressure guage if the pressure is above 7 psi install a regulator and control for 6.5 to 7 psi. Had the same problem running a 750 speed demon in that the pressure was to high hence the bowl levels were to high (floats couldn't control it) and engine ran really rich. Your "engine" combo is good otherwise but your rear gears are a different matter. I'd go either 3.55 or 3.91. JMO

Oh, one other thing, I'm running a 4 hole 1 inch spacer on top of my Weiand single plane, it really helped with the off idle response.

Terry

 

[dgc333]

IMHO, you have an engine set up for racing but are crusing around with it. You have mis-matched your components to the use.

I would go to a stock heat range plug gaped at the stock 0.035" (later you can go wider to take advantage of the MSD.

You well may need more timing than 32 degrees when cruising. Consider using a vacuum advance distributor to get some more timing under light load conditions. It is not unusal for a stock distributor to have intial+mechanical+vacuum to be in the 50+ degree range.

The carb suggestions everyone has made are a good place to start but my one experience with a Demon was it was big rich when operating off the transition circuit. Likely not a blown power valve since new holleys and all Demons have protection. You will likely need to play with air bleeds to correct that. Again if the car is a cruiser a holley 3310-2 Vacuum Secondary 750 would be a better choice.

 

[ramcharger]

Are you using the ballast resistor with the MSD unit?

 

[taco502001]

fuel pressure is set at 6psi with afpr, float level is set right above the bottom of sight bowl.

I am going to try hotter plugs with a wider gap see how the car likes that. From what I can gather this is more setup for racing and with my cruising style driving its mismatched. I cant afford it right now but i am going to try a carb with vaccum secondaries distributor will remained locked out might put more advance it and put a timing retard on the msd system for ease of starting the car. At least I have a starting point now

 

[rumblefish360]

taco, what plugs are you running now again? You really shouldn't have to go to far from a stock heat range. Cooler is prefered by a step or two. I gapped my plugs @ .55 with the MSD. That was the best result gap.

When money allows, I'd look at a 750 carb and a tighter performing, higher stall converter.

I think the 3.55's can do it, but it will be a close call. The engine is struggling to release power. The cams 244 @ .050 is a bit stout for the gears.

 

[taco502001]

Well what sucks is I am not the one who assembled this motor or performed the work, I mean i know how to change and read plugs etc.... But i do not have time tools or knowledge to do much else. You might call me crazy but for ***** and giggles I pulled the ngk fr7s on the drivers side and cleaned them up best I could I raised the gap from .022 the shop had them at to .045 and put back in. Since my exhaust is true dual no x pipe or h pipe I started car up and let it run for a short time. I noticed alot less carbon and **** out of drivers side exhaust than compared to passengers. Eventually I will put some ngk fr5s in and gap those .045/

And no it did not clean up with highway driving that is what seemed to cause the problem, I think between those problems there and the carb I can get this car to work. But I think the way I drive mostly street driving and cars setup is mismatched I am going to try a edelbrock victor/performer with a quickfuel carb with vaccum secondaries. The timing locked out should have no effect but produce a hotter and more full burn at idle but I agree I will try and get it to 38* total

But for now it looks like I have a classic scenario of mismatched parts, If I want to make this intake and carb work I think I need a more radical cam, heads, converter, and gears. But if I want a more street friendly setup I need a smaller single or good dual plane intake, smaller carb with vaccum secondaries and still more gear though

 

[ramcharger]

.018 gap is ridiculously small. Your power valve may be rated too high causing the flooding you're seeing on the highway. You don't need a ballast resistor with a MSD box and coil. Hope this helps.

Oh yeah, stay away from the shop that gapped your plugs.

 

[taco502001]

Yeah ballast resistor has been bypassed it wasn't originally and then I had to fix that problem. What sucks is this guy was suggested to me by scott brown of straightline performance. But yeah I will change the plugs gap them right, make sure wires are good and msd and everything is wired up properly. Then I will go from there and find out the jets sizes and etc... and try to get carb setup.

I am looking at cam/head/gear/converter change or keeping gears and etc... and getting different intake and carb and retune the car

 

[ramcharger]

You're headed in the right direction taco! Good luck and keep us updated. A dual plane like the Edelbrock Performer RPM might be worth looking into and will help your engines street manners quite a bit. I wouldn't give up on that carb yet, I would replace the big Weiand Team G first.

 

[redfastback]

remember to only do a 1-2 things at a time and then test drive it. this way you not changing too many variables at once and not know the reason why it magically fixed itself. this way you can see what did and did not change things for the better. good luck.

imo, pitch the demon for a holley.

 

[ramcharger]

remember to only do a 1-2 things at a time and then test drive it. this way you not changing too many variables at once and not know the reason why it magically fixed itself. this way you can see what did and did not change things for the better. good luck.

Agreed!

 

[thecarfarmer]

I thought I knew a little about reading plugs, too.

...I mean i know how to change and read plugs etc.... But i do not have time tools or knowledge to do much else....

But I'd check this article out: it opened my eyes to a couple things:

http://www.4secondsflat.com/Spark_plug_reading.html

This damn internet... every time I think I know a bunch about something, I find out that there's a bunch more I don't know about it...

Happy hunting.

-bill